Parasitoid insects face considerable trade-offs in locating suitable hosts within complex environments. Apocephalus paraponerae (Diptera: Phoridae) locates its host ant Paraponera clavata (Formicidae: Ponerinae) using olfactory cues. Here, comparing two populations of A. paraponerae, I describe differences in host location cues between two sites, Barro Colorado Island (BCI) in Panama and La Selva Biological Research Station in Costa Rica. At La Selva, A. paraponerae uses the ant mandibular gland products 4-methyl-3-heptanone and 4- methyl-3-heptanol in host location, but does not do so on BCI. I propose that higher colony density of P. clavata causes A. paraponerae to use more species-specific cues on BCI. I also discuss how geographic variation in host location cues could lead to allopatric speciation.